What determines the stresses in a structure?
One of the difficulties of answering this question is that we never actually see anything that has no stresses in it. We will return to that point later.If we take a beam and lower it on to its supports, or we remove the centring from an arch, the structures will deflect because they are being exposed to different forces from the original ones. How far will they deflect, and what stresses will build up in them? What happens is that every part of the structure will move relative to its neighbours until the entire structure is in equilibrium, meaning that there is no net force on any part. When any object changes shape, which is referred to as being strained, it will experience stress, which in most structural materials is proportional to the strain.Here is an example in which a weak material has been used to exaggerate the effects. A block representing a building presses on a piece of foam plastic representing the ground. The compression of the ground generates exactly enough pressure t
